1. Field of the Invention
The present invention relates an electric heater comprising N groups of heating elements which change their temperature due to electrical power consumption.
2. Description of the Background Art
Electrical heaters are known for automotive applications. Within air-conditioning systems electrical heaters are widely used to heat up the air before entering the passenger compartment especially at cold-start conditions and in case the cooling liquid of the cooling liquid circuit of the combustion engine is not sufficiently heated by the combustion engine. Usually after the cooling liquid has almost reached the steady state temperature the electrical heater will be switched off by a control unit. Therefore the electrical heater is regarded as auxiliary heater in addition to a heater core supplied by a cooling liquid of the cooling circuit of the combustion engine. For electrically driven vehicles the mentioned heater is the main heater of the vehicle.
In automotive vehicles using combustion engines as main drive unit the electric power circuit typically uses a low-voltage configuration. Applications for pure electrical vehicles or hybrid-drive vehicles comprising an electric drive unit and a combustion engine are using high-voltage circuits in order to provide the necessary electrical power to the electric drive unit. Low-voltage means for sake of clarity a voltage below 50 V, high-voltage means a voltage of about 50 V or more, especially above 100 V up to 300 V or 500 V.
With regard to high-voltage applications safety is a very important issue within automotive applications. For the use of high-voltage systems in automotive applications the system has to be designed in such a way that nobody may be injured even in case of a failure of the system.